Sins of the Future
by Hitokiri-san
Summary: After their trip into the future, Tsuna and co. were faced with the Byakuran of their time. Now they must decide what to do with the white-haired maniac.


**Sins of the Future**

_A Katekyo Hitman Reborn! fan fiction by Hitokiri-san _

**A/N: This is written for the KHR Fest, Round IV on LJ, dwelling on the question of "after the disastrous TYL arc, what do the Vongola or the kids do with TYE! Byakuran?" **

**Irie might get off easy, since despite everything that happened, he ultimately proved to be an ally; the same could not be said for Byakuran. **

**Would they kill him? Byakuran, technically, hadn't done anything to anyone yet; and with the sealing of the Mare rings, he probably wouldn't be able to again. So it would be somewhat a murder in cold blood. Letting him go didn't seem a safe choice, either. **

**I've intended this to be Byakuran-centric, but Gokudera (who arguably suffered the most angst in the TYL arc, the poor dear) insisted on having the spotlight, so here you are. **

* * *

"_We've got rid of you_," Gokudera, who'd thrown himself in front of Tsuna after the initial shock, snarled. "The Tenth banished you in that battle! So what are you doing here?"

"Tsunayoshi-kun _killed_ me in the _future_," Byakuran corrected with a bright grin, making two points in a single sentence. Tsuna visibly recoiled, wide brown eyes dilating at the reminder; Yamamoto's grip on his shoulder tightened, a reassuring gesture. "I just haven't reached that future yet."

"Then you'll just have to die again!" the _Sistema _C.A.I was out in a blast of bright, angry crimson; the bone shields forming a tight semi-circle around Tsuna – because like _hell_ he'd let Byakuran get to his boss again, this time. Without hesitation, he fired, Storm flames blazing a trail towards the white-haired man.

Knowing Byakuran, he'd honestly expected him to conjure up a protective barrier or something. He didn't expect the man to barely scramble out of death's way, his Namimori uniform – why did all the nutcases like to sell themselves off as highschoolers? – badly singed from the impact. From the stunned expression on Tsuna and Yamamoto's faces, they hadn't expected that either.

Idly, Gokudera remembered that he'd blown off half of Namimori Middle's rooftop in his fury. Hibari was going to be_ spitting mad_ when he found out.

"What happened to your inhuman superpowers?" he asked, point blank, as the Millefiore boss picked himself up from the ground, unfazed. Byakuran rolled his eyes at him childishly, as though he was being particularly stupid.

"Come on, Hayato-kun," he chided, and Gokudera half-wanted to blow his face off just for even calling him that, "Uni-chan sealed the Mare rings' power with her life in _that_ future. That means no universe-skipping power for me. You can't possibly forget that."

It was unnerving, the casual way he referred to that life-and-death battle. _We nearly died a few times over_, _all of us,_ thought Gokudera. Byakuran was right, he mused with a touch of relief, and he was an idiot for forgetting. He frowned as he remembered something important.

"No, wait, you shouldn't have received the Mare rings at this stage. You shouldn't even_ know _about what happened in the future."

"The Vongola and the Cavallone are not the only ones to receive a vision of the future," Byakuran commented, as if he was amused at the idea, and smiled at the three of them with that sunny expression of his. "It wouldn't be fair, would it."

It absolutely would, by Gokudera's standard, if it meant that they didn't have to deal with a world-destroying lunatic of Byakuran's calibre.

"Why are you here, then? I doubt that Namimori has anything for you. It isn't like it's a particularly interesting place." Yamamoto's voice rang out from behind him, dark and grave and dangerous, and Byakuran perked up, craning to look at him from where he stood behind Gokudera.

"Takeshi-kun," he greeted, enthusiastically, and seemed to consider his question seriously. "Why, to see Tsunayoshi-kun, of course! It would be interesting to meet the person who's going to kill you, don't you think?"

"Stay the hell," Gokudera gritted out, and it was taking all his will to just stand there and _not_ kill the man there and then. _Not in front of the Tenth_, who looked as though he'd taken a punch to his guts at Byakuran's words. The kind-hearted boy wouldn't approve, not when the Millefiore mafioso had already lost his power. "_away_ from the Tenth."

Byakuran gave them a cryptic smile, lavender eyes crinkling into a slit, and they all knew that it wasn't the end.

* * *

At least Byakuran wasn't in their class. That was a meagre comfort in and of itself; to be honest, he had no idea what he'd do if the psycho was in their classroom. He thought, idly, that this goddamn school had a penchant for admitting foreign Mafiosi and random assassins, as though it was actually fond of them. It did not occur to him that he himself was one of the school's odder admissions.

Reborn was in their classroom, however, dressed up as a freaking_ schoolbag_, his toddler face sticking out in a round patch on the bag's pouch.

"Stop being all jittery, it's unbecoming of a Guardian," Reborn told him in that poised way of his, hanging from a hook on the side of Gokudera's desk. "What will your boss think of your behaviour?"

Like this isn't bothering the Tenth already, the Storm Guardian wanted to say, but didn't. You just _didn't_ argue with the arcobaleno.

"Byakuran is targeting the Tenth. You heard him," he gritted through his teeth, and resolutely refused to look at Reborn. "I will not allow this. I will _not_."

His failure in the future-that-will-not-be was still too fresh, a bitter aftertaste of the whole nightmare, and he'd do anything in his power to prevent that. The infant scrutinized the dark, steely glint of his grey-green eyes – _like a brewing storm, _he noted_ - _and the determined set to his shoulders. He knew what that meant.

"Byakuran is now powerless," he told the Storm Guardian, musingly, "he can't do much to Tsuna."

Once, he might have been convinced, because Reborn was omniscient and could never be wrong. But he'd learnt, once, that his Boss had been shot down by simple _guns_. The world was never the same again.

"Byakuran might resort to…other means." _Poison and traps and guns and tricks, because Byakuran was cunning and insane like that, and because the Tenth believed in the good of everyone. He wouldn't have seen it coming._

Gokudera could see it coming, though. And as Tsuna's guardian it was his job to see that it never happened. _Again_, he thought with a grimace.

"Reborn-san," he hissed, lethal, and the hitman's beetle-black eyes stared back at him impassively. They'd both known it would come to this. Reborn agreed; he wasn't trying to dissuade him further. "I'll take care of this. Byakuran won't be a bother anymore."

"Tsuna wouldn't approve," Reborn said, not a protest but a reminder. He was a hitman, Gokudera remembered, suddenly; he understood the need of putting a bullet into someone's head, just to keep the Family safe.

"The Tenth doesn't need to know," he muttered, small and unsure because he'd never once lied to Tsuna before, and the notion distressed him beyond belief. But it was something that needed to be done, and it was something he would never regret, even if it meant that the Tenth would be furious at him if he knew.

"You're pampering him too much. He'll need to know someday," Reborn snorted, and watched as Gokudera blanched. It would appear that Storm Guardian was trying to hide the uglier side of the mafia from his boss forever. Stupid child. "And it might as well be today."

"Not now," Gokudera half-stated, half-pleaded, "the Tenth is a kind, noble man. He doesn't like to kill. He'll never be able to stand it."

Reborn raised his brows at him, but didn't comment. Across the classroom, Tsuna absently prodded his face with the back of a pencil, trying to figure out their trigonometry classwork.

* * *

So he planned.

He'd pulled Yamamoto aside in between classes, asking him to escort the Tenth back home after school. The baseball idiot had cheerfully nodded, airy laugh echoing in the corridor in a way that made Gokudera want to bash his face in.

S_ober the hell up, can't you see that the Tenth is in danger? _he was about to snarl, but then Yamamoto spoke.

"Don't want him running into dangerous people, right?"

And that was when he knew Yamamoto understood the gravity of it all. All he needed to do, afterwards, was leave the Tenth in his care (_Reborn-san and the trusty Rain, no matter how he didn't want to admit that; together they wouldn't fail him_), and blast Byakuran into so many little pieces no one could ever find him again.

It was a failsafe plan.

Except that Tsuna already _knew_.

"Gokudera-kun," the Tenth's grip on his forearm was uncharacteristically tight, almost frantic, and Gokudera felt his resolve cracking at the edges. "Aren't you walking me home today?"

"M-my apologies, Tenth. I…have certain things to attend to today." Like find goddamn Byakuran and blast him sky high, but Tsuna wouldn't like that, so he didn't say.

Those wide eyes narrowed, suspicious, and Tsuna hung onto him relentlessly, as though he was afraid of Gokudera taking off in a sudden. It was like all the times when the brunette had latched onto him when he was about to blow things or people up.

"I need your help in some of the Maths homework due tomorrow! Won't you help me?" his boss said in a rush. Then his gaze shifted out of focus, as though he was remembering something, and he grabbed Yamamoto without looking.

"Yamamoto, let's do the homework together."

It was Tsuna's way of grounding them both, so that they wouldn't rashly go after Byakuran, and Gokudera understood. Still, there was nothing he could do in the face of the Tenth's blatant request.

"If that is…what the Tenth wants."

Even if he couldn't finish off Byakuran in the dark, he could be in close quarters with the Tenth this way. With him and Yamamoto flanking the Tenth all the way home, even the white-haired maniac would have his hands tied.

The three set off, chatting like it had been a normal school day, and no murdering psychos were out for their lives.

* * *

Things weren't going to be that easy, and he knew it.

Gokudera felt his breath catch as he saw Byakuran – _Byakuran _– coming out of the Tenth's house, all uniform and smiles, as though he had just been visiting a friend.

_Reborn-san_, the Storm Guardian thought in abject mortification. Reborn-san was supposed to be guarding everyone in the Tenth's house. Byakuran shouldn't even be able to set foot in this place.

Shock was evident on the Tenth's face. _Mom and the kids, _he could hear his boss thinking, and felt the same panic rising in his chest.

"I told you to _stay away_!" Gokudera heard himself screaming as he nudged Tsuna behind the protective wall of Yamamoto, stalking towards the Byakuran with deadly purpose. Byakuran did not budge, eyes crinkling in false merriment as he stood before the Sawada household. As though he had every right to be there.

"You sick bastard," he hissed at Byakuran, hand poised over the boxes lining his belt, "I'm going to_ kill you_."

It would be a bloodshed. He'd_ intended_ it to be a bloodshed, consequences be damned. But then Reborn dived down from the upstairs window to land on his head, and the impact managed to distract him for a bare second.

"Wait, Gokudera," the infant said, crossing his legs languidly on the Storm Guardian's head. Gokudera could feel the vague reprimand in the toddler's stance – _didn't you say you're going to finish him off?_, it said.

"Reborn-san! Is…"

"Everyone's okay," Reborn fingered the rim of his fedora, expressionless, "Maman just treated him to tea."

Gokudera gaped, the incredulity of Tsuna's mom treating _Byakuran _to tea failing to sink in at the moment. But Nana didn't know; she had always been a little air-headed in this aspect. She'd probably think that she's playing host to another of Tsuna's…unique friends.

"It was such good tea, too," Byakuran acquiesced, hefting his schoolbag onto his shoulders absently, "you have a good mother, Tsunayoshi-kun."

"You…why are you here?" Tsuna's voice came from behind Yamamoto, shaky and unsure, and Byakuran only raised a brow.

"To see how Tsunayoshi-kun's life is like, of course!" was the bright reply, and Byakuran took two steps forward, so he could see Tsuna better. Yamamoto's smile was all sharp edges and protectiveness, even as Tsuna recoiled further behind him. "I don't know much about you, you see, apart from what I got from the flashbacks."

"What is it to you?" Gokudera barked, and Byakuran only shrugged, letting the question slide off his shoulders like water.

"Wouldn't you be curious? Getting visions of a person who you've never met, who you know is going to kill you in ten years' time. Wouldn't you want to know more about that person?"

"I'm…I'm not going to kill you," Tsuna rebutted, faintly, as though he was going to be sick. Yamamoto gripped his shoulder, firm and reassuring, and it was at times like this that Gokudera was glad that the baseball idiot existed, despite how infuriating he could be most of the time.

"Not in this timeline, maybe," the white-haired man nodded sagely, sounding like they were in the middle of an academic discussion about alternate universes and not a dramatic facedown, "you've sealed the Mare rings. There's not much point to killing me anymore."

"What are you trying to do to the Tenth?" the Storm Guardian interjected, tone deep and interrogating, "talk, or you _won't_ be here in ten years' time, I assure you."

This question, for some reason, seemed to _delight_ Byakuran. How the world could produce nutcases like this man was beyond Gokudera's understanding.

"Nothing," he announced, mirthful, and blinked when silver-haired teen practically exuded disbelief, "it isn't as though I can do anything anyway. The Vongola is taking me away to someplace far away, or so they say."

_Ah._ So it was why Reborn wasn't blowing his brains out on the pavement. Gokudera sneaked a sideway glance at the Tenth, who looked visibly distressed at the information, and bit out, "serves you right, you murdering bastard."

"_I_ never killed anyone," the white-haired man countered mildly, uncaring, "I never exactly _did_ anything, in this timeline, in this world."

"Oh, you will, if you have the power to," Gokudera narrowed disdainful grey-green eyes at him, fingers flexing over the rim of his boxes, "don't speak as though you are _innocent_."

"If mere intentions could make a murderer," Byakuran mused, offhandedly, "what does that make Tsunayoshi-kun?"

Tsuna slid down against Yamamoto as his legs gave out under him, shivering violently, and Gokudera realized, too late, that the damage had been done.

"Hey –"

"You goddamn piece of – "

"You are a good kid, Tsunayoshi-kun; I won't harm you," Byakuran cut them off effortlessly, sending a crooked smile Tsuna's way, "Vongola is going to put me behind lock and key for life, so you don't have to worry."

It was said with blatant disregard, as though the thought of his own life imprisonment didn't quite interest him. Byakuran walked past the three of them, steps light and meandering, before he turned back almost as an afterthought.

"But between you and me, Tsunayoshi-kun, I think you're more of Vongola's prisoner than I am. I can already see the years before you."

"Are you done, Byakuran?" Reborn's voice was cool and cutting, a predator about to pounce, and Byakuran only shrugged, waving lazily at the trio on the footpath.

"_Goodbye_, Tsunayoshi-kun," it was a parting curse, lingering thickly in the air like miasma. The white-haired man boarded the black limo waiting on the porch – _Reborn had arranged for it, Tsuna thought absently – _and the Sun Arcobaleno followed, leaping through the vehicle's open window with controlled ease.

"Wait! _Reborn_!" Tsuna's plea was wrought with tearful tremors, and Reborn turned briefly at him, beetle black eyes devoid of empathy.

"This is out of your hands now, Tsuna. Stay out of this."

"No!" Tsuna sprung when the limo drove off, or tried to; his two closest Guardians held him back, ushering their struggling friend back into the house, where Nana waved them in cheerfully.

"It has to be done, Tenth," Gokudera met the overflowing terror of his boss' eyes, and tried to put the matter as gently as he could, "he could destroy the world - you know he already did, numerous times."_ He killed you, and I will never forget._

"He did _nothing_! He's an innocent!"

"They aren't going to kill him, Tsuna, it's just like the way it was with Mukuro and Xanxus," Yamamoto soothed, like the rain he derived his title from, "it's the best that could happen."

* * *

They guarded Tsuna side by side as the boy drifted off to an exhausted nap at the bedside table at his room, overwhelmed by guilt and terror and sadness.

Laying a jacket over the Tenth's shoulders, Gokudera remembered his first kill, dark alleys and handmade explosives and carefully calculated physics. Yamamoto thought of the future-that-will-not-be, regrets and lost lives and a lifetime devoted to the underworld.

"We're here. We'll always be here," Yamamoto told the sleeping Tsuna, steadily. For once, Gokudera did not berate him for disrupting the Tenth's sleep.

The ship Byakuran boarded never reached the island it was supposed to reach. The man was not the Vongola boss' son, after all. And no one in Vongola – not even Iemitsu or Reborn - had any realistic hope of being able to tame someone as perilous as Byakuran.

Meanwhile, Gokudera and Yamamoto saw Tsuna on his way home after another school day, unaware that out of three Skies of the _trinisette_, theirs was the only one left alive.

_~end_


End file.
